The earliest true fungal lineages likely resembled modern chytrids. Aquatic Produced flagellated (swimming) spores Fed by external digestion (already a defining fungal trait). This is before large animals dominate land.
As the Holomycota fungal lineage began to diverge, they increasingly relied on growth rather than motion to survive. To better exploit solid substrates, they reinforced their cells with rigid chitin. From soil, decaying matter, and eventually land itself, they extracted a material that let them push into their environment instead of swimming through it. Early-diverging fungi such as chytrids kept their “rear‑engine” flagellum to navigate thin films of water, but most fungi gradually abandoned swimming altogether. They survived by using hydraulic pressure to drive their thread‑like hyphae forward, effectively growing their way into new territory rather than motoring there.